Paint calculator
A 12 × 12 ft room with 8 ft walls, one door and two windows needs 2 gallons for two coats (1.7 gallons exactly at 400 sq ft per gallon). Enter your room, and the coverage printed on your can.
Room four walls
Doors and windows edit to match yours
Measure the opening, trim included if you won't paint the trim with the wall color.
Paint
400 sq ft per gallon is typical label coverage, but check your can. For example, Benjamin Moore lists 400 to 450 sq ft per gallon for Regal Select Eggshell (technical data sheet). We use the low end.
How the gallons are worked out
- Wall areaAdd the length and width of the room, double it to get the distance around, and multiply by the wall height: 2 × (12 + 12) × 8 = 384 sq ft.
- Minus openingsSubtract each door and window. One 3 ft × 6 ft 8 in door is 20 sq ft and two 3 × 4 ft windows are 24 sq ft, leaving 340 sq ft.
- Coats and coverageMultiply by the number of coats and divide by the coverage on the can: 340 × 2 ÷ 400 = 1.7 gallons, so you buy 2.
The coverage on a can is measured on a smooth, primed surface. Rough plaster, bare drywall, textured walls and big color changes soak up more paint, so they get less than the label says. Benjamin Moore's data sheet for Regal Select recommends two coats for full color and says previously painted walls can take one or two.
Source: Benjamin Moore Regal Select Eggshell N549 technical data sheet (spread rate per gallon 400 to 450 sq ft; two coats recommended). Quarts: NIST Handbook 44, Appendix C.
Gallons for common rooms
8 ft walls, one 3 ft × 6 ft 8 in door, two 3 × 4 ft windows, two coats at 400 sq ft per gallon.
| Room | Paintable wall area | Exact gallons | Buy |
|---|---|---|---|
| 10 × 10 ft | 276 sq ft | 1.38 | 2 gallons |
| 12 × 12 ft | 340 sq ft | 1.7 | 2 gallons |
| 12 × 15 ft | 388 sq ft | 1.94 | 2 gallons |
| 14 × 16 ft | 436 sq ft | 2.18 | 3 gallons |
| 15 × 20 ft | 516 sq ft | 2.58 | 3 gallons |
| 20 × 20 ft | 596 sq ft | 2.98 | 3 gallons |
Questions people ask
- How many square feet does a gallon of paint cover?
- It depends on the product, so read your can. As one example, Benjamin Moore's Regal Select Eggshell data sheet lists 400 to 450 sq ft per gallon. This calculator starts at 400, the low end, and you can type any number from your label.
- Do I need two coats?
- Plan on two when you change color or paint new drywall. Benjamin Moore recommends two coats for Regal Select to get full color, and says a previously painted surface can be finished with one or two.
- Should I subtract doors and windows?
- Yes. They are not painted with the wall color, and a 3 ft × 6 ft 8 in door alone is 20 sq ft. Subtracting them can save you a quart or a gallon in a room with many windows.
- Is it cheaper to buy quarts?
- The list shows both whole gallons and a gallons-plus-quarts mix. When the mix comes to 3 quarts, compare prices: three quarts hold 3/4 of a gallon, so if they cost about as much as a gallon, buy the gallon and keep the rest for touch-ups.
- How much paint for the ceiling?
- Tick "Also paint the ceiling" in Room size mode. The ceiling is the room's length × width, and it is listed on its own line because most people use a separate ceiling paint.